The disclosed invention is directed to a roll change device for removing and inserting work rolls in a four-high rolling mill stand, and in particular, the invention is directed to retrofitting an existing four-high rolling mill stand with a roll change device that will simplify removing worn work rolls from the mill and inserting refurbished or new work rolls into the mill. The roll change device is capable of being installed on an existing four-high mill stand without making modifications to the roll stand housing, and it is particularly suited for retrofit in an existing four-high rolling stand where the work roll chocks are captured within the backup roll chocks. The roll change device is installed in an existing mill stand with relatively minor modifications being made to the existing roll chocks and with no modifications being made to the mill stand architecture and housings.
State of the art rolling mills include counter-opposed upper and lower work rolls supported in bearing chocks that are mounted on opposite sides of the rolling mill stand. In a four-high mill, the upper and lower work rolls are also supported by respective upper and lower backup rolls that are also supported in bearing chocks that are mounted on opposite sides of the rolling mill stand housing. In some instances, the chocks of the work rolls are at least partly captured within and laterally restrained by the backup roll chocks.
Normal practice in a rolling mill operation dictates that the work rolls must be periodically removed from service for either grinding to restore the working surface, or for other maintenance on the rolling mill stand. During such shutdowns, the work rolls are removed from the mill stand along the axial direction of the rolls. In a where the work roll chocks are captured within the backup roll chocks, the current state of the art includes a variety of methods for removing and/or installing the work rolls in the mill. Such methods include roll removal devices suspended from cranes in combination with heavy counterweights that balance the weight of the work roll(s). These crane-handled roll change devices are labor intensive, requiring a significant downtime to perform work roll changes.
Retrofitting a four-high rolling mill stand with a roll change device is expensive, time consuming, and generally requires significant modifications to the mill stand housing and related components. For example, U.S. Pat. No. 6,038,905 to Cherubini describes a device to remove working rolls in a four-high roll stand where the work roll chocks are contained within the backup roll chocks. The roll change device comprises a lifting system including actuators that are mounted below the lower backup roll chocks and anchored to stationary parts of the mill stand at a location within the space defined between the lower backup roll chocks. The lifting system further includes extension rods attached to and extending between the actuators and sliding rails that is raised or lowered in response to operating the lifting system actuators. A pair of sliders extends longitudinally from one side of the mill stand to the opposite side of the mill stand. When the actuators are operated to move the extension rods in a vertical direction, the sliding rails are either a raised so that they engage the sliders attached to the lower work roll chocks, or they are lowered to a rolling or working position. The vertical moving sliding rails engage the work roll chock sliders and lift the work rolls for removal from the rolling stand.
Although it appears that the Cherubini roll change device may be an improvement over the prior art, the inventor has failed to recognize a number of inherent problems associated with his device. For example, the Cherubini device requires the lift system and actuators to be either fastened to the mill housing or to a slider used to remove the lower backup roll from the mill stand. In the first instance, if the lifting system is attached to the mill housing, changes and modifications must be made to the mill stand architecture at a location below the lower backup rolls.
In instances where the lifting system is fastened to a slider, it would be necessary to provide a complex slider system for lower backup roll removal. Such a slider attached lifting system would be expensive to implement and would require major changes to the mill architecture.
Furthermore, the sliding rails disclosed in the 905 patent are limited in length to the distance between the inboard sides of the lower backup roll chocks. In other words, the sliding rails cannot extend outboard of the chocks. This makes it necessary to provide a slider that is solidly fastened to the lower work roll chocks in order to enable removal or insertion of a work roll in the mill stand. Such a slider arrangement complicates the disassembly and reassembly of lower work roll chocks and thereby exacerbates maintenance and work roll grinding operations. Additionally, the xe2x80x9csolidlyxe2x80x9d fastened slider attached to the lower work roll chocks may restrain the chocks and prevent proper and independent axial and lateral alignment with the necks of the lower work roll as well as with the corresponding surfaces of the backup roll chocks. Such improper alignment can have disadvantageous effects on the work roll bearings and the quality of the product being rolled.
A roll change device, according to the invention, comprises a pair of spaced apart lower work roll lift assemblies, each lift assembly including an actuator and lift-rail arrangement positioned within a four-high rolling mill stand to remove and insert work rolls, in combination with a removable, self-contained roll staging platform assembly positioned adjacent the mill stand to receive worn work rolls and to deliver new or refurbished work rolls. The actuator and lift-rail arrangement is fastened to opposing inboard facing surfaces of the spaced apart lower backup roll chocks, the actuator and lifting rail arrangement improving roll chock alignment and bearing life when compared to past roll change devices, as well as simplifying operations related to the removal and insertion of work rolls when retrofit into an existing four-high rolling stand. The removable self-contained roll staging platform provides means for delivering and removing work rolls, and the platform is removable as a single unit from its working position within the mill floor to provide millwright access to the lower backup roll pit. The present roll change device invention is particularly suited for retrofit into an existing four-high rolling mill stand with relatively minor modifications to the existing mill parts and little or no modifications to the mill stand housings, the retrofitted mill stand and roll change device reducing maintenance related downtime and extending bearing life when compared to earlier roll change devices that are solidly fastened to the work roll chocks.